With recent downsizing and high density of electronic equipment, a double-sided or multi-layered circuit board is employed more frequently than a conventional single-sided board, as a circuit board on which electronic components are mounted, and a high density circuit board allowing a larger number of circuits to be integrated in a circuit board is developed.
For the high density circuit board, instead of drilling of holes (through holes) in the board, which is conventionally operated, employment of laser machining capable of faster and more fine machining is developed (Y. Yamanaka et al. “Excimer Laser Processing In The Microelectronics Fields”, for example). Also proposed is a circuit board in which layers are connected using fine holes made by laser and such connection means as conductive paste (shown in Japanese Patent Application Non-examined Publication No. H06-268345, for example).
In the technique of making fine holes and connecting layers using conductive paste, a few foreign substances may cause contact failure.
In this technique, the substrate material is drilled together with a film bonded thereto and the film is used as a mask for filling the conductive paste into the fine holes. Therefore, all the substrate material including the film must be kept clean.
However, both drilling and laser machining produce a large amount of dust and debris from the cutting process, and this dust and debris may adhere to the board material and close the holes for electrical connection. In addition, it is also possible that a little dust in air may close the fine holes. To solve this problem, the board material is cleaned before the conductive paste is filled in the holes. However, because complete cleaning of the holes by a dry cleaning method is very difficult, such new wet cleaning methods as ultrasonic cleaning are employed. These methods require drying after cleaning, in order to remove the moisture absorbed from the periphery of the machined holes or the outer ends of the board material.
As shown in FIG. 4(a), mask films 2a and 2b are bonded to substrate material 1. Provided at an end of substrate material 1 are peel off leading parts 3a and 3b for stripping mask films 2a and 2b after the conductive paste is filled. The leading parts 3a and 3b are made by stripping a part of each of mask films 2a and 2b. 
Because of such a structure, when sheets of substrate material 1 are stacked one on top of another and dried by heating using a conventional hot air convection method as shown in FIG. 4(b), B-stage epoxy resin in the board material melts and stripping leading parts 43a and 43b and substrate material 1 melt together again, as shown in FIG. 4(c). Therefore, it is difficult to treat and sufficiently dry a large number of sheets at a time.
A small number of sheets could be treated with a vacuum dryer. However, it takes long time to dry a large number of sheets because sufficient latent heat cannot be given to the material under vacuum and thus energy sufficient to remove the moisture cannot be added.
In improving reliability of connection in circuit boards, wet cleaning is more effective than dry cleaning. However, insufficient drying after cleaning would significantly affect the reliability of connection and insulation.
For this reason, moisture must be removed completely. However, the conventional method is not efficient and may possess problems e.g. causing more damage to the board material.
The present invention is directed to realize a board material having high-quality fine holes and to provide a method and a system of manufacturing highly reliable circuit boards at low cost.